Since the early 1980s, adjustable gastric bands have provided an effective alternative to gastric bypass and other irreversible surgical weight loss treatments for the morbidly obese. The gastric band is wrapped around an upper portion of the patient's stomach, forming a stoma that restricts food passing from an upper portion to a lower portion of the stomach. When the stoma is of the appropriate size, food held in the upper portion of the stomach provides a feeling of fullness that discourages overeating. However, initial maladjustment or a change in the stomach over time may lead to a stoma of an inappropriate size, warranting an adjustment of the gastric band. Otherwise, the patient may suffer vomiting attacks and discomfort when the stoma is too small to reasonably pass food. At the other extreme, the stoma may be too large and thus fail to slow food moving from the upper portion of the stomach, defeating the purpose altogether for the gastric band.
In addition to a latched position to set the outer diameter of the gastric band, adjustability of gastric bands is generally achieved with an inwardly directed inflatable balloon, similar to a blood pressure cuff, into which fluid, such as saline, is injected through a fluid injection port to achieve a desired diameter. Since adjustable gastric bands may remain in the patient for long periods of time, the fluid injection port is typically installed subcutaneously to avoid infection, for instance in front of the sternum or over the fascia covering one of the oblique muscles. Adjusting the amount of fluid in the adjustable gastric band is achieved by inserting a Huber tip needle through the skin into a silicon septum of the injection port. Once the needle is removed, the septum seals against the hole by virtue of compressive load generated by the septum. A flexible catheter communicates between the injection port and the adjustable gastric band.
While the injection port has been successfully used to adjust gastric bands, it would be desirable to make adjustments noninvasively. Insertion of the Huber tip syringe is typically done by a surgeon, which may be inconvenient, painful, or expensive for the patient. In addition, a skin infection may occur at the site of the insertion of the syringe. Consequently, it would be desirable to remotely control an adjustable gastric band.
Infusers have been implanted in patients for controllable dispensing of a liquid drug, such as described in U.S. Pat. No. 4,581,018. A cylindrical metal bellows has a movable end that is drawn toward its nonmoving end by a lead screw that passes through the bellows into a threaded hole of the case. Thus, the volume of the metal bellows accumulator was affirmatively controlled by the number of turns made by the lead screw, avoiding inadvertent overdoses in dispensing a liquid drug.
However, infuser pumps are intended to be driven in only one direction whereas adjusting constriction of the gastric band often requires that fluid be removed from the elastomeric balloon to reduce constriction as well as the reverse direction to increase constriction.
In addition, it is becoming increasingly important that implanted devices in general be operable and nonresponsive to a strong magnetic field as the use of magnetic resonance imaging (MRI) becomes more common. An MRI machine produces a strong magnetic field, which may be up to 3.0 Teslas in flux density, that will impart a strong magnetic force upon any ferromagnetic material. Devices such as electrical motors may be damaged by such magnetic fields or the patient may feel discomfort. Moreover, ferromagnetic material may create artifacts in the radio frequency (RF) return that the MRI machine detects and processes by disturbing the magnetic field.
In an implanted peristaltic pump, such as described in U.S. Pat. No. 6,102,678, a piezoelectric drive system is used to provide a rotary device that is lightweight, compact with very small axial volume and with the particular desirable feature of being practically unaffected by external magnetic influences. While a peristaltic pump differs substantially from a bi-directional metal bellows accumulator/pump, it would be desirable to incorporate similar features of MRI compatibility in a bi-directional infuser pump.
Consequently, a significant need exists for a reversible pump suitable for medical implantation to remotely adjust a gastric band.